The major goals of this research plan are to define the domains within the matrix protein region of the HIV-1 Pr55Gag molecule which interact with cellular membranes, and to characterize the transport pathway taken by Pr55Gag in order to reach the plasma membrane assembly site. The first specific aim is to identify the domains within the matrix protein region of Pr55Gag which contribute to interaction with cellular membranes. Initial experiments will identify the domains within matrix which contribute to membrane binding using a novel membrane flotation assay. The role of multimerization of MA in regulating membrane interactions will next be examined. Phosphorylation of MA on serine or tyrosine may be a reversible regulator of MA protein interactions with cellular membranes. The second specific aim is to define the role of phosphorylation of the MA protein in membrane binding, and to identify the phosphorylation sites which alter its membrane-binding capacity. Experiments included in the third specific aim will define the domains within matrix that determine specific transport of the molecule to the plasma membrane. Intracellular transport of wild-type and mutant Gag proteins will be examined using subcellular fractionation techniques, immunofluorescence microscopy, and electron microscopy. Transport-deficient Gag protein mutants will be utilized to identify potential sites of early Gag-Gag interaction within the cell. The ability of actin polymerization to influence particle assembly sites will be dissected and the responsible domains within Pr55Gag mapped. The long-term objectives of this line of research are to understand the molecular basis of HIV assembly processes in sufficient detail to allow the design of specific inhibitors of assembly events.